Wide-angle lens



sa. GPTiGsz Patented Apr. 21, 1931 UNITED STATES Nausicaa WALTER G.WOLFE, OF GREENWOOD, MASSACHUSETTS, ASSIGNOR T WILMOT R. EVANS, TRUSTEE,OF BOSTON, MASSACHUSETTS WIDE-ANGLE LENS Application filed May 18,

My present invention relates to what I may term wide angle optics asincluding a broad field in which much work has been done but in whichapparently much remains to be done. My invention is capable of variousembodiments and a great variety of uses as it involves certainprinciples heretofore not recognized which I have been able to lay holdof and apply with a considerable degree of success.

Many optical propositions present such a wide and diversified field thatdiscussion may best be limited to some particular application,especially where new principles are involved, and I have thereforeselected the art of wide angle projection as the general province withinwhich I will attempt to define my discussion and within that provincewill particularly point out the applicability 2o of my invention topictorial projection as upon a screen for observation by the human eye.There are many reasons why wide angle projectionis very desirable, andin fact, 1t is one of the things that has been long and consistentlysought. One of the constant difficulties throughout all such endeavorhas been that of marginal distortion or the socalled pin cushion orbarrel effect by reason of which the margin of the field of p rojectionhas been so distorted that anything like pictorial or photographicminut-ias have either been lost or so badly distorted as to spoil theeffect.

This difficulty has been recognized to be due principally to sphericalaberration and achromatism. The optical difficulties of correcting thesesingly and conjoint-ly in wide angle optics have been so great that ithas been heretofore supposed to be impossible to get practical results;that is to say, it has been, so far as I am advised, impossible toproject a picture of large size from an ordinary slide or motion picturefilm from a short distance. A characteristic and extreme case of suchproj ection is that of the moving picture which is projected from a verysmall photographic transparency under very high magnication to a sizecapable of being observed by a very large audience. This has been thereason that the projector has been placed in or be- 1927. Serial No.191,590.

hind the audience, in spite of the terrible and perfectly obvious riskof iire. Back stage projection was an obvious desideratum. It was an oldpractice from the earliest days of picture projection of comparativelylarge size lantern slide plates, but with the limitations of spacebehind the proscenium arch and the requirements of high magnification ofminute motion picture film, practical results were utterly impossible.

In applying my invention to this field, I devised a novel lens or lenssystem which I will proceed to describe as both illustrative and as anembodiment of great value and of immediate usefulness and importance.Inasmuch as it involves a factor of safety for human life I make mydisclosure with all promptness and without those delays which prudencewould dictate in confirmatory experimentation and scientificinvestigation which would aid me to more fully establish novelprinciples which are doubtless present, but which I doubtless onlyimperfectly sense at this time. In this I rely upon the protection ofthe law and that discretion of the courts on which I must depend inawarding me full protection against such lack of detail as the emergencyof my disclosure may necessitate.

Owing to the nature of my invention the drawings are necessarilysomewhat exaggerated in order to make the details of optical finesseobservable and understandable, but I believe such drawings will bereadil comprehended by those reasonably sln'lle in the art and they dowith some pictorial exaggeration fairly represent actual optics made byme and under successful operation. Throughout the specification anddrawings like reference characters are employed to indicatecorresponding parts, and in the drawings:

Fig. l is a face diagram of a lens in' accordance with my invention.

Fig. 2 is a curve diagram of such a lens section.

'Fig 3 a diagrammatic section of a lens form.

Fig. 4 is a similar view of a modied form thereof, and

Fig. 5 a modified form of aspheric correction.

Wide angle projection lenses for detail such as pictorial o-rphotographic minutiae have generally been considered as impossibleoptics from the practical point of view. This was due to the extremespherical aberrations involved, as well. as to chromatic difficulties.Optical science has, of course, known how to correct for aberration andhow to correct for color. Nevertheless, to the best of my knowledge andbelief this knowledge has not been deemed applicable to producepractical results as required in this art. This is due to thedifficulties in conditions and requirements between large lenses such asastronomical lenses and relatively smaller optics such as the projectionart requires. Furthermore, in the projection art there is the extremedifficulty of deliniteness in correction sufficient to maintain detailwithout disturbing continuity of pictorial effect.

Referring to Fig. 1, the lens 2 has for eX- ample a central sphericsurface as indicated as a central zone Z. Beyond that surface is amodified surface or annular portion indicated by 2. Such an annularsurface has been generally known in optics but generally in connectionwith large lenses where an aspheric surface is produced by working downthe margins of a spheric. I mention this because while such a generalsurface has been known and while it might be though to have atheoretical application to my present invention, it is not a practicalsurface utilizable as such and my invention consists in part in a modi-{ication of this surface to get those results which make a new andrevolutionary combination of projector screen and even theatre itselfpossible.

At this point attention is invited to the diagram shown in Fig. 2. Thismay be considered as the line of curvature from the center `outwardlyO-O indicating the optical axis. `In this we may consider the portionbetween @the radii R as a spheric and the elements .a of the broken lineextended beyond as indicating the plurality of surfaces each moredivergent from the curvature of the sphere jand each preferably of anincreasing length as indicating a zone of greater breadth. Instead,therei fore, of the continuous curvature of the lens l. i margin outsideof the spherical portion Z, my

lens has what may be considered as a plurality of denite annularsurfaces constituting as a whole a general hyperbolic trend of thesurface but different therefrom from the fact that they are definiteindependent optical denite annulae necessarily results in the projectionof differentiated rings on the intercept, as for example, on the screen.By making these optical annulae, however, sufficiently narrow so thatthe rings on the intercept are of a width Within the range of distinctvision, I find it possible to use these definite surfaces e to eliminatespherical aberration to an extent that it is ignorable and without inthe slightest disturbing the interpretive value of pictorial eifectsdistributed zonally. By my invention I am able to get as clear andundistorted a picture at back stage distance (say 19 or 20 feet) as atprojection from the back of the hall (at say or 80 feet).

In the matter of optics involved, it will be seen that the successivesurfaces e produce in general that hyperbolic tendency heretoforeattained by the very delicate correction of a spherical lens. My lensesmay therefore be considered generally as aspherics but the mathematicaldeiiniteness of the successive annulae must be borne in mind. I do notmean by this that the annulae need to be maintained in true planes northat they intersect each other sharply. I mean they must be ofprogressive divergence considered as planes and preferably of increasingwidth but of a suicient narrowness to give on the picture a zonal widthwithin the limits of distinct vision.

The lens illustrated in Figs. 1, 2 and 3 is such a lens intended for usewith a projection objective, such for example as that used in theordinary moving picture machine. It is a negative and the lens describedwould be mounted in advance of the said projection objective and about 8inches from it, or at such position as to eliiciently receive theprojected beam. The member 2 is a bow silicate crown n/d 1.5126 v 62.7.The curvature of the zones Z, a, are respectively for Z 8.230 c/m. Forover the zone .e asgindicated by the broken lines, embraced by thebracket in Fig. 2, the curvature would be for .e2 r 8.721; for .e3 r9.000; for .e4 r 9.310; for .e5 r 9.620; and for e (not applied to thedrawing for lack of space) r 9.931. .el would be 1 10.000, as r 10.414.

This may be taken as a typical modification but is given as an entirelypractical one for the purpose used, i. e. for moving picture projection.The diameter of the lens described is 12.70 c/m. The contact concavityof the member 2 has a complete radius 8.230 c/m and receives the planoconvex member 3 which has a curvature of that radius spherical and incontact in the form shown. The rear face is plano and its thickness atcenter is 2 c/m. This is flint glass n/d 1.6041 v 37.8. The meandispersion of the member 2 is C to F .00818. Partial dispersion .00245,C to D; .00573 D to F; .00460 F to G. For the iint member 3, meandispersion .01599 C 3g. GP! sw! to F; partial dispersion .00457 C to D;.00142 D to F; .00969 F to G.

A standard projector lens which is usually of three-inch focus projectsa picture about twenty-one feet square at a distance of seventy oreighty feet. For such I provide a system consisting of a crown member 2which I preferably form as a double concave lens the rear or first facehaving full negative curvature including a central surface Z surroundedby a series of annular surfaces .e as described in connection with 2.The second surface would be a weak negative. The Hint member 3 as shownis a plano-convex. A second similar system may be used in practice tosecure the desired corrected divergence and can be made to give astandardized size of picture of approximately twenty-one feet square ata distance of only seventeen feet. It may be noted by comparison thatwith the ordinarily projecting lens at such a distance a picture ofapproximately live feet square could be attained.

In the form shown in Fig. 4 the third surface, i. e. the flint member 3amay have its surface modified as at Zl1 to give the effect of the zonalcorrections z of Fig. 3.

In Fig. 5 the modified form carries the annular surfaces Za on the Hintmember but in such form there is more difficulty in correcting color.

My invention is, of course, capable of all the variations of opticaldesign common to lens production and is capable of all the chromaticcorrections by the relative figuring of the Hint member 3 and the crownmember 2. My invention may be practiced with any translucent screen andmy combination of projector and lens system, screen and theatre may bemade to suit any varieties of architecture or settin arrangement.

What I there ore claim and desire to secure by Letters Patent is 1. Anegative achromatic lens inclusive of a concave side having a centralspherical surface and a plurality of concentric ring-like surfacesdisposed outwardly of said central spherical surface, said ring-likesurfaces being spherical and progressively increasing in focal lengthtoward the edge of the lens.

2. A negative achromatic lens inclusive of a concave side having acentral spherical surface and a plurality of concentric ring-likesurfaces disposed outwardly of said central l spherical surface, saidring-like surfaces being spherical and progressively increasing in widthand in focal length toward the edge of the lens.

3. A negative achromatic lens inclusive of a concave side having aplurality of concentric ring-like spherical surfaces progressivelyincreasing in focal length toward the edge of the lens.

4. A negative achromatic lens inclusive of a concave side having aplurality of concen- Draftsman gressively increasing in focal lengthtoward the edge of the lens.

In testimony whereof I aflix my signature.

WALTER Gr. WOLFE.

